Hormonal Contraception and Endometrial Thickness in IVF/ICSI Cycles: A Multicentre Historical Cohort Study

Objective: To study the association between previous use of levonorgestrel intrauterine system (LNG-IUS) and endometrial thickness (EMT) in women undergoing in vitro fertilisation (IVF)/intracytoplasmic sperm injection (ICSI) cycles. Design: Multicentre historical cohort study. Setting: Eight Danish public and private fertility clinics. Population: 12786 women aged 18–46 years contributing with an EMT measurement from 22 464 different IVF/ICSI treatment cycles between 2000 and 2021. Methods: Exposure was previous use of LNG-IUS, combined oral contraceptive pills (OCPs), progeste-only pills (POPs), no/other contraception or combined, cumulated use of contraception when more contraceptives had been used during the inclusion period. Further, ever use of LNG-IUS was categorised into 0–3 years, > 3–6 years, > 6–9 years and > 9 years. Mixed effect logistic regression adjusted for age, BMI, smoking, educational level, total FSH dose and fertility clinic was used. Main Outcome Measure (s): EMT (< 7 mm ≥ 7 mm). Results: Statistically significantly higher odds of EMT ≥ 7 mm were found for OCPs [odds ratio (OR) 3.53 (95% confidence interval (95% CI) 1.29–9.65)], POPs [OR 6.43, (95% CI 1.45–28.63)] and no/other contraception [OR 6.67, (95% CI 2.37–18.74]) relative to LNG-IUS in IVF/ICSI cycles. Further, all duration categories of ever use of LNG-IUS were associated with statistically significantly lower odds of obtaining an EMT ≥ 7 mm compared to no/other contraception. Conclusions: In this study, previous use of LNG-IUS was associated with decreased endometrial growth in women undergoing IVF/ICSI.